Study Finds Branched Yeast Mannoproteins Keep Wine Tannins Suspended During Aging

A study published in the journal Carbohydrate Polymers reports that the carbohydrate structure of yeast-derived mannoproteins can change the way they interact with grape seed tannins, a finding that could matter for how wine behaves during aging.

The research focused on colloidal stability, a term used to describe whether small particles stay evenly dispersed in a liquid or clump together and fall out of solution. In wine, that process can influence sediment formation, clarity, texture and some aspects of taste. The study found that not all mannoproteins act the same way. Their effect depended on the structure of the polysaccharide portion of the molecule, especially how branched it was.

Mannoproteins are compounds released from yeast cell walls during fermentation and aging. They are already known to play a role in wine development, but the new work examined more closely how differences in their internal structure affect their behavior when they meet tannins from grape seeds. Tannins are central to the texture and astringency of wine, and they also contribute to how a wine changes over time.

To test the interaction, researchers extracted four mannoproteins with different polysaccharide profiles and incubated them with grape seed tannins under laboratory conditions designed to resemble wine. They then analyzed the mixtures with dynamic light scattering, atomic force microscopy and fluorescence spectroscopy. Those tools allowed the team to measure the size of the complexes that formed, observe their physical shape and assess how the compounds bound to each other.

The results showed a clear pattern. Mannoproteins with more highly branched polysaccharide structures tended to form smaller complexes with the tannins. Those smaller complexes were more stable and less likely to aggregate into larger particles. By contrast, mannoproteins with less branched structures produced larger aggregates that were more prone to sedimentation.

That difference matters because the size and stability of these complexes can influence whether tannins remain suspended in the wine or drop out over time. According to the paper, more branched mannoproteins appear to offer greater protection against tannin precipitation, helping preserve colloidal stability during aging. Less branched forms did not provide the same effect and were associated with larger assemblies that could reduce clarity and alter texture.

The study also linked these interactions to the sensory profile of wine. If tannins stay better dispersed, that can affect mouthfeel and the way the wine evolves in the bottle or barrel. The paper did not present a consumer tasting trial, but it said the improved colloidal behavior seen with certain mannoprotein structures could support a more favorable sensory outcome during aging.

The work adds detail to a long-standing question in wine science: why some wines remain stable while others develop more haze, sediment or changes in texture as they mature. It suggests that the answer is not only the presence of mannoproteins, but the specific architecture of the polysaccharides they contain.

For the beverage industry, the findings may be especially relevant in winemaking, where producers routinely try to manage tannin balance, clarity and aging performance. The study points to a possible route for doing that more precisely by considering the structural profile of yeast-derived polysaccharides, whether through yeast selection, aging practices or additive strategies. Any practical use would still need testing in commercial cellar conditions, since the current work was done under simulated wine conditions in the lab.

The results may also interest researchers studying other drinks in which polyphenols and polysaccharides affect stability, appearance or mouthfeel, although this study examined grape seed tannins specifically and did not test beer, spirits or other beverages.

The paper describes the interaction as a structural effect at the molecular level. In simple terms, the more branched mannoproteins seem to create smaller and more stable assemblies with tannins, while less branched ones allow the formation of larger particles that are more likely to settle. That helps explain why yeast-derived compounds can have different outcomes in the same type of wine.

The authors said a better understanding of these interactions could help refine wine aging processes. Their data suggest that choosing mannoproteins with suitable polysaccharide characteristics may improve colloidal quality and help maintain desirable wine properties over time.